Pennsylvania GOP Rep. Charlie Dent is serving his last week of Congress, having submitted his formal resignation effective May 12.

Dent, co-chairman of the moderate Republican Tuesday Group, had announced on April 17 that he would be resigning sometime in May. His decision to leave Congress early came as he neared a decision on several professional opportunities he had been considering for his retirement.

House retirements are a staple of each election cycle. But the decision by three moderate Republicans not to seek re-election is worrying party members, already nervous about holding the majority in 2018.

“You hate to have an open seat in what you know is going to be a bad year,” said Oklahoma Rep. Tom Cole, a former chairman of the National Republican Congressional Committee.